Hi John

A couple more thoughts:

To cut down your backup window SWA (Save While Active) can be a good choice.
Stop everything on your system until you reach the SWA checkpoint for the
critical libraries then restart processing. Getting a checkpoint doesn't
take all that long in my experience and makes the backup window a much more
manageable thing.

Virtual tape has some advantages in this scenario in that you have protected
yourself against a media failure invalidating the save. As I understand it,
using tape you would have to restart the entire process from the beginning,
including establishing a checkpoint again.

Evan Harris

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of John McKee
Sent: Thursday, 4 September 2008 8:33 a.m.
To: midrange-l@xxxxxxxxxxxx
Subject: RE: Virtual tape

My question was well answered. I knew that both virtual tape and save files
took up space. Obviously, for decent performance, a separate ASP is almost
mandatory. What I had wondered was whether multiple processes could be
used to
speed up backup. I was thinking that critical libraries could be
backed up to a
SAVF and later transferred to tape with the system being available for
users. Short answer is >maybe<, as availability of DASD is still a
factor, as I
thought surely it would be. Years ago, I wrote a CL that prioritized the
libraries to be backed up. Once the high priority libraries were safely on
tape, other libraries were kept locked and users were allowed back in.
As each
remaining library was backed up, the lock on the library was released.
That did
cut downtomie considerably, on that ancient system.

Thanks for the information on disk usage.

John McKee

Quoting Pete Massiello <pmassiello-ml@xxxxxxxxxxxx>:

If you have an LTO-3 or better device, you will not be happy with the
performance results of Virtual tape, unless you have A LOT of arms. MANY


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of John McKee
Sent: Wednesday, September 03, 2008 2:45 PM
To: Midrange Systems Technical Discussion
Subject: Virtual tape

To back up 100G of DASD to virtual tape, would you need 100G of DASD for
virtual tape? Or possibly a better question: Does virtual tape utilize
compression, thus not requiring quite as much space as if data was simply
copied disk to disk?

How would the size be calculated?

How does virtual tape compare to using a save file or multiple save files?

John McKee

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